A series is given, with one number missing. Choose the correct alternative from the given ones that will complete the series.
400, -200, 100, ? , 25, -12.5

A series is given, with one word missing. Choose the correct alternative from the given ones that will complete the series.
Oxygen, Toil, Arouse, Arson, Tenuous, ?

Select the odd letters from the given alternatives.

Select the related number from the given alternatives.
7.25 : 7.75 :: 9 : ?